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.TH RANDOM_R 3  2016-03-15 "GNU" "Linux Programmer's Manual"
.SH NAME
random_r, srandom_r, initstate_r, setstate_r \- reentrant
random number generator
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "int random_r(struct random_data *" buf ", int32_t *" result );

.BI "int srandom_r(unsigned int " seed ", struct random_data *" buf );

.BI "int initstate_r(unsigned int " seed ", char *" statebuf ,
.BI "                size_t " statelen ", struct random_data *" buf );
.br
.BI "int setstate_r(char *" statebuf ", struct random_data *" buf );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR random_r (),
.BR srandom_r (),
.BR initstate_r (),
.BR setstate_r ():
.RS 4
/* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
.RE
.ad b
.SH DESCRIPTION
These functions are the reentrant equivalents
of the functions described in
.BR random (3).
They are suitable for use in multithreaded programs where each thread
needs to obtain an independent, reproducible sequence of random numbers.

The
.BR random_r ()
function is like
.BR random (3),
except that instead of using state information maintained
in a global variable,
it uses the state information in the argument pointed to by
.IR buf ,
which must have been previously initialized by
.BR initstate_r ().
The generated random number is returned in the argument
.IR result .

The
.BR srandom_r ()
function is like
.BR srandom (3),
except that it initializes the seed for the random number generator
whose state is maintained in the object pointed to by
.IR buf ,
which must have been previously initialized by
.BR initstate_r (),
instead of the seed associated with the global state variable.

The
.BR initstate_r ()
function is like
.BR initstate (3)
except that it initializes the state in the object pointed to by
.IR buf ,
rather than initializing the global state variable.

The
.BR setstate_r ()
function is like
.BR setstate (3)
except that it modifies the state in the object pointer to by
.IR buf ,
rather than modifying the global state variable.
.SH RETURN VALUE
All of these functions return 0 on success.
On error, \-1 is returned, with
.I errno
set to indicate the cause of the error.
.SH ERRORS
.TP
.B EINVAL
A state array of less than 8 bytes was specified to
.BR initstate_r ().
.TP
.B EINVAL
The
.I statebuf
or
.I buf
argument to
.BR setstate_r ()
was NULL.
.TP
.B EINVAL
The
.I buf
or
.I result
argument to
.BR random_r ()
was NULL.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw27 lb lb
l l l.
Interface	Attribute	Value
T{
.BR random_r (),
.BR srandom_r (),
.br
.BR initstate_r (),
.BR setstate_r ()
T}	Thread safety	MT-Safe race:buf
.TE
.SH CONFORMING TO
These functions are nonstandard glibc extensions.
.\" These functions appear to be on Tru64, but don't seem to be on
.\" Solaris, HP-UX, or FreeBSD.
.SH SEE ALSO
.BR drand48 (3),
.BR rand (3),
.BR random (3)
